Formation of modified nucleosides in DNA by chemical alkylation, is known to be a potent mutagenic and carcinogenic event. Moreover, biological methylation of cytosine is important in transcription and in protein-DNA recognition. Under methylation of control sequences may even trigger oncogenic transformation. In addition, DNA conformation, and conformational flexibility are fundamentally important to DNA function and are influenced by the presence of modified nucleosides. To begin to understand the detailed molecular bases of these phenomena model systems - specifically modified oligonucleotides - are necessary. The long term goal of this project is development of the synthetic strategy and procedures to make synthesis of specifically modified oligonucleotides a practicable endeavor. To begin to accomplish this goal we will devise high-yield routes to modified nucleosides of importance for incorporation into oligonucleotides. These will include 1. deuterium derivatives of deoxyadenosine, deoxycytidine and deoxyguanosine, 0-alkylated derivatives of thymidine and guanosine, 6-amino-deoxyguanosine, and 5-methyl deoxycytidine. In all cases emphasis will be placed on devising routes amenable to large scale synthesis so that the modified nucleosides produced can be used for oligonucleotide synthesis. In order to incorporate these modified nucleosides into oligonucleotides we will devise new synthetic strategies that are more nucleoside efficient than present approaches. For example, whenever possible we will develop one-flask reactions for protection of these monomers. In addition, the synthesis of 0-6 alkyl guanosines we are working on gives access to a new class of protected deoxyguanosine derivatives which should eliminate the degradation normally observed with guanine nucleosides. Successful protection of guanine should enable us to recover and reuse oligonucleotide blocks with little loss, which would allow use of polymer supported methods for oligonucleotide synthesis. Polymer support synthesis is fast but always requires use of a substantial excess of the incoming block. We will also examine use of cobalt (III) ion as a phosphate protecting group which would act as a polar "handle" to aid in separation of condensation mixtures.